Electrical receiving, translating, or repeating circuit.



G. A. CAMPBELL.

ELECTRICAL RECEIVING, TRANSLATING, 0R REPEATING CIRCUIT.

APPLICATION FILED, JUNE 5,1916.

1,227,1 14. Patented May 22, 1917.

I 3 SHEETS.SHEET I. fig! L1 msm JIICZ Ze I xG. I 2w [7712677 for: v G .14. Campbell per aw? fltzornpy.

- s. ApCAMPBELL ELECTRICAL RECEIVING, TRANSLATING, 0R REPEATING CIRCUIT.

APPLICATION FILED JUNE 5, I9I6- 1,227,114. PatentedMay 22, 1917 3 SHEETS-SHEET 2- W $10000 3:30P fioook W 4 C2 2 r5161 2 F5] 2 G. A: CAMPBELL.

APPLICATION FILED JUNE 5.1916.

Ll' l l l l l L ELECTRICAL RECEIVING, TRM-JSLATING, 0R REPEATING CIRCUIT.

Patented May 22,1917.

a E J IM I I I L 3 SHEETS-SHEET 3.

fi l l l enonen 'A. current PHONE mn'riiniseniern contra-nit, A GOBPOnA'rION on NEW YORK.

To all whom it may concern: I

Be it known that I, Gnonen A. CAMPBELL, residing at'Montclair, inthe county of Essex and State of New Jersey, have invented cer- 5; t'ain Improvements in Electrical Receiving,

Translating, or Repeating Circuits, of whic thefollowing is a specification.

This invention relates to electric wave filters and more particularly to the combinaceiving, translating or repeating devices. Its

object is to protect such electrical receiving, translating or repeating device from currents of all frequencies lying outside a preassigned range or ranges of frequency and to transmit thereto without appreciable diminution currents of all frequencies lying within. said range or ranges of frequency;

The object of my invention is attained by inserting between a signaling circuit, such as a telephone line, and the receiving, translating or repeating device an electric wave filter or the serial combination of a plurality of wave filters "adapted to. transmit with all frequencies lying Within a preassigned range or ranges-of frequency while attenuatand approximately extinguishing currents of all frequencies lying outside the limits of said preassigned range or ranges. The wave filterwhich I prefer to "use is not claimed in this application, but constitutes the subject matter of my co-pending appli- 4 cation, Serial No. 40,057, filed July 15th, '35

1915, of which this application is a division.

My invention, though it may find expression in many embodiments has, common to all, the broad idea of the combination of a translating device, such, for example, as a repeater, and a wave-filter in the nature of a connecting line having an impedance element or elements in series with the line andan impedance element or elements in shunt across the line, the values of the impedance elements being so proportioned that the structure will transmit with small or negligible at;

all frequencieslying within specified orrpreassigned limits or ranges while attenuating tionof electriowave filters and electrical re--' small-or negligible attenuation currents of Specification of Letters Patent. Patntd 1\Ia,y22, 1917.

Original application filed July 15, 1915, Serial No. 40,057. Divided and this application filed June 5, 1916. Serial No. 101,845. r

My invention in one or more of its embodi- 'ironrcrara, NEW 'annsni assrenon roamnmcm 'rnnnments in signaling circuits hasimportant applications in connection with wireless telegraphy, wireless telephony, multiplex high frequency wire telephony, composited telegraph and telephone lines; in il qfact broadly in connection with any signaling system employing translating devices where in it is highly important that means be provided for selecting a range or band of'frequencies necessary for the transmission of intelligence while at the sametime excluding from the repeater currents of all other frequencies.

My invention is illustrated in the accompanying drawings in which Figure l is a diagram illustrating the broad form of wavefilter which is a component element of my invention; Figs. 2, 3, 4, 5, 6 and 7 are diagrams illustrating different forms of wave-filters adapted for combination with repeatersy Figs.- 8 and 9 show curves illustrating the characteristic performance of the wave-filter; and Figs. 10 and 11 are diagrams showing my invention embodied in telephone repeater circuits.

Like reference characters refer parts throughout the several figures of the drawings.

Referring to Figs. 1 to? inclusive, each wave-filter 1 1 1 1 1 1, 1 is composed of a plurality of identical sections 2%, 2", 2,

2 2 .2", 2 respectively, each including lumped impedance in series with the line and lumped impedance in shunt across the line, Said impedance may be provided by condensers, C C or by inductance coils L L or by a suitable combination of both, there being at least, for each section of the wave- -filter, an inductance element in series .with the line and a capacity element in shunt .across theline or vice versa. Thus in Fig. 1 "showing the preferred form of wave-filter, there are, for each section, both a condenser 0 and an inductance coil L infseries with ther line and a condenser C and an inductance coil L in parallel in shunt across the line; In said figures, as wellas in the other acters C and C are used to designate simiand substantially extinguishing currents of lar eiements, that is condensers, the suball frequencies lying outside such limits.

afiixed to the-reference letter indi figures of the drawing, the reference char .elements for each section'areincluded as follows :-In Fig. 2, there is a condenser in series with the line and a condenser and an inductance coil in parallel in shunt across the line; in Fig. 3, a condenser and an inductance coil in series with the line and an in ductance coil in shunt across the line; in Fig. 4, an inductance coil in series with the line and a condenser and an inductance coil in parallel in shunt across the line; in Fig. 5, a condenser and an inductance coil in series with the line and a condenser in shunt across the line; in Fig. 6, a condenser in series with the line and an inductance coil in shunt across the line"; and, in Fig. 7, an inductance coil in series with the line and a condenser in shunt across the line. Said Figs. 1 to 7 inclusive, merely show typical forms of the invention and are not intended to illustrate all of the possible modifications thereof.

-By assigning suitable values to the con-v densers C C and the inductance coils L L in said Figs. 1 to 7 inclusive, the structure, if inserted as a connecting line between a source of electro-magneticenergy and an electrical receiving, translating or repeating device, will transmit to the latter sinusoidal currents lyingwithin preassigne'd ranges or bands and will at the same time effectively protect the receiving, translating or repeating device from currents of frequencies lying outside the 'preassigned ranges or fre-.

quencies.

The fundamental principles underlying the wave-filter and the manner of applying the same so as to provide a structure adapted for embodiment in this invention will now be set forth.

It is a well known fact, that in a uniform transmission line containing uniformly dis- .tributed resistance, inductance and capacity,

the attenuation of current along the line is a phenomenon wh1ch is caused by resistance dissipation and becomes zero when the resistance becomes zero. In a periodic structure, however, containing lumped series impedance and'lumped shunt impedance, high attenuation may exist even when the resistance is practically zero. This attenuation is due not to resistance dissipation but to in volved reactions among the impedance units of the structure- The reactions and interactions, taking place in the structure and determining the character and attenuation at tending transmission of periodic currents,

are so involved as to make desirable the use of mathematical formulae in elucidating the laws governing the electro-magnetic phenomena taking place in the structureand in particular in laying down rules of design whereby any one, skilled in the art, may construct the electric wave-filter embodied as a component element in this invention.

For the purpose of deriving the mathematical formulae pertaining to the theory of the wave-filter, assume a structure consisting of a series of sections, each section having an impedance Z in series with the line, and an impedance Z in shunt across the line. Letting J n denote the circuital current flowing in the nth section of the structure, J the current flowing in the ('n-1)st section, and J01) the current flowing in the (n+l)st section, and applying Kirchhoffs law to said currents and circuits, it follows that Z J +Z (J J +Z (J J =0 By various rearrangements this equation may be written as,

of I, it follows that for propagation in either direction:

J Z =e (1) In the foregoing equations, e denotes the base of Naperian logarithms, and F denotes the propagation constant of the structure. The value of I is, so far, unknown but may be determined by substitution of the above values of n and J in the above difference equation, whence,

e +e=-l+2 cosh r= %:)+1 (2) v "Referring-to equation (1), if F is not r a pure imaginary, the current. value is diminished or attenuated in transmission lute values of .J, and Job) are equal, and

.hence the current suffers no attenuation in transmission from section to section but f only a change of phase. 10

/' I shall be a: pure imaginary.- It may be,

i The condition, /then, for unattenuated transmission is that shown from equation "(2) that the condition for un'attenuated' transmission is that I 1 shall between 11.

' Hence the limiting values of the frequency I Z above g ven, ltis evident that equations (a) 'havev as the variable of unknown the for free transmission are given by the symbols For the structure shown in Fig. 1, it evident that the series impedance 1 L C p PQ and the shunt impedance 2 main. Z 1 i 2P In these formulae [2 ,is Qicf where f is the frequency in cycles per second, and i is the imaginary quantity Referring to the texpressions for Z and value of 79., There are four roots or four values of 7) which will satisfy said equa- "tions which roots will be denoted by 9 p 'and p Said roots have the following values i It will be observed that these. four limit- I ing values of p or 2m are in geometrical proportion, and that the contra p p 'the frequencies for the upper ban he between p and p and for the-lower band between 19 and 130/2 Equations (5) to (9) inclusive'are fundamental to and by their aidthe electrical constants of. the wave filter may be deter-' mined; Fromfsaid fundamental equations,

simplifiedformulae for different: structural embodiments of the wave-filter may beds rived; as will hereinafter be pointed out.

Referring to thedrawings, Figs. 8' and 9 show the character of transmission through the structure illustrated in Fig. .1. In said Figs. 8 and.9,f f f f represent frequencies corresponding to 0 0 2 20 respectively.; In Fig. 8; the ordinates are received currentsawhlle the abscissae are sae frequencies.

frequencies. Fig. 9 has as its ordinates at I tenuation values per section and as abscis The full line curves refer: to the ideal structure in which the resistance of the impedance units is quite negligible, while the broken line curves show the departure from the ideal case due to resistance in the structure. In any case the resistances are made sufiicientlv small to be practically negligible.

It is not always desirable to transmit .two bands of frequencies, and as a further refinement, my invention also contemplates'a wave-filter which will transmit freely all frequencies lying within asingle band of specified limits. As will hereinafter be more fully set forth the structures shown in Figs. 2 to 7 inclusive, will function as a single band wave-filter, and the structure, shown in Fig. 1 may be made to so funct1on.-

' Reference to Fig. 8 and to equations (5), (6), (7) and (8), shows clearly that if the two bands of free transmission are made to coalesce or merge into one by setting f zf or if one of the bands is pushed eut gier relegated either to infinity or to Zero, there remains one single band of free transmission for finite frequencies. The first form of single band wave-filter is a ttained 1 by making f =f or L C L C This form will be referred to as a filter having coalescent or confluent bands.

The second method of realizing a single band wave-filter is attained by relegating the upper band to infinity or the lower band to zero. Reference to equations (5), (6), (7) and (8), shows that one band is relegated to infinity if L or C :0; while the other band is rele ated to zero if L or C 00. Obviously, rom the foregoing, the single band may also be attained by making L =C =0, orby making L =C =cn.' It will be understood, of course, that an infinite inductance or a zero capacity are equivalent to an infinite impedance, and, hence, a circuit through the same may be regarded as replaced by an open circuit, on the other hand a zero inductance or an infinite capacity are equivalent to a zero impedance, and, hence, they may be regarded as in effect short circuited.

It thus appears that there are, in general, seven ways of reducing the double band wave-filter to a single bandwavefilter, namely:

(a) Making the two broad bands coalescent or confluent by setting L G L C (b) Relegating one band to infinity by making L :0;

(c) Relegating the other band to infinity by making 0 :0;

(d) Relegating one band to zero by making 0 00 (e) Relegating the other band to zero by making -00;

(f) Making L =C O and thereby transmitting freely all frequencies above a specified value; I

(g) Making L =C =oo and thereby transmitting all frequencies below a specified value.

Design formulae will now be given by applying which any one skilled in the art, may construct a wave-filter which will freely definite, preassigned; bands of frequencies while attenuating all frequencies lying outside these bands.

Considering first the general form ofthe double band wave-filter, let it be required to design a filter which shall freely transmit all frequencies lying between the limitalso between transmit a definite, preassigned band or l (7) and ei] ei or 2 ;ftan a] Formulae III and IV are equivalent. A structure so designed or proportioned that its electrical constants satisfy formulae (I) (II) and (III), or (I), (II), and (IV). complies with the above stated requirements for freely transmitting frequencies lying between 7", and f constituting one band and between f and f constituting the second band, while attenuating and sensibly extinguishing currents of all frequencies lying outside these bands.

The rules of design of the single ban l wave-filter will now be considered, the different cases, treated in order.

(a) Confluent bands, in which case L C =L C This form is shown in Fig. 1, it being understood that the structure shown in said figure may be made to function as a single band wave-filter by making L C zL G that is by causing the two bands to coalesce. If the frequencies to be freely transmitted are to lie between the up per limiting frequency 7", and the lower limiting frequencies f the design formulae are:

(b) Relegating one band to infinity by making L =0 in which case the structure of the wave-filter assumes the form shown in hereinbefore stated, being Fig. 2. If the limiting frequencies of free I transmission are .(upper limit) and f (lower limit), the design equations for this form are dia) (c) Relegating one band to infinity by making 0 :0, in which case the structure of the wave-filter assumes the form shown in Fig. 3. If the limiting frequencies of free transmission are f (upper lixriit) and f (lower limit) the form are Eddi (d) Relegating one band to zero by making-C co, in which case thewave-filter is 10 of the form shownin'Fig. 4. Let the limiting frequencies be i and f, and the design formulae are:

tafitl le design formulae for this (a) Relegating one band to zero by making L 0 in which case the Wave-filter assumes the form shown in Fig. 5. Let the limiting frequencies of free transmission be f tand f and thedesign formulae are:

v(g) Making. L,==C =-;oo, in. which case a the wave-filter assumesthe form shown in Fig.- 7 and freely transmits all, frequencies below a specified superior limit. If the rsuperiin" limit-ingf requency is specified fas -'f the design formula is: v

4,5 It will be observedjfrom the foregoing de- .Isign formulae that there is always one im- ..pedanc'e-elementwhose value is a matter of choice. The value of this-element may be determinedv from conveniemiv of design or maybe made to satisfy some other specified requirement, such as, for instance, that the line shallhave a'd'efinite impedance at a particular frequency. It is further. evident that the particular 'form of single band wave-filter is a matter of choice and thefselection of any particular form may be left to the requirements of a particular design.

It will further be understood that the number of sections of the. Wave-filter willdepend on the degree to which it-is desired to extinguish the currents to be filtered out. If the number ofsectipns us doubled the ratio of the current offahy particular frequency entering the filter to the current of that frequency leaving the filteris approxi mately squared;

As an example of the application of the foregoing design formulae, let it be required to design a filter which shall transmit all frequencies lying between 200 and 2000 cycles per second. Any one of the forms shown in Figs. 1, 2, 3, 1,5 may be employed or the two forms shown iii-"Figs. 6 and 7 connected in series. Let it be assumed that convenience or other considerations lead to the selection of the type ofwave-filter'shown .in Fig. 1. Applying design formulae (l?) and (IF), applicable to this type of single band wave-filter, and substitutmg therein for f and f the above assigned Values 200 and 2000, respectively:

and

L2 1 200 2 ii ifawi ma Therefore the above stated requirements are satisfied if 11 0 11 0 (.635) 10- and- "of all frequencies lying between 200 and 2000 cycles-per second. The attenuation cons tant per section at a frequency of 2200 cycles per second, for example, is found from equation (2) by computation to be .98.

Hence, from equation (1), the ratio of currents in adjacent sections is 2.67 approximately, and if five sections are employed the current 0f2200 cycles in the 5th section is less than 2% of its value in the first secvtion, While currents of frequency lying between 200 and 2000 cycles per second are practically unattenuated,

In the light of the foregoing description of the wave-filter my invention as illustrated in Figs. 10 and 11 will now be described. Referring to Fig. 10 there is shown a two-way two-repeater circuit employing vacuum tube repeaters in'combination with wave-filters of the type shown in Fig. 1. It is to be understood thatthe wave-filters shown 14. The input side in Figs. 2, 3, land 5 might be equally well employed. In said Fig. 10, a two-way tworepeater-set consisting of two symmetrical halves is shown, and hence the same parts in the two halves of the set are designated by the same reference characters. The terminals 3, 4 and 3, 4 connect the repeater set in series with the through telephone line (not shown). At each end of the set are the secondary windings 6, 6 and 7, 7 of a re peating coil, of which the windings 5 constitute the primaries. Across the middle of the windings6, 6 and 7 7 are connected the conductors 8, 9 which lead to the filters 1*. The other end of each filter is closed by a non-inductive resistance 10. The vacuum tube repeaters 11 are of a well-known type comprising a grid 12, filament 13, and plate of the repeater 11 is shown as bridged across half. of the non-inductive resistance 10. The battery 15 heats the filament 13 through the adjustable resistance 16. Across the filament 13 and plate 14 is bridged the battery 17 in series with-the high inductance coil 18. The function of the coil 18 is to allow the passage of direct current, but to prevent the passage of alternating current of telephonic frequencies. In parallel with the battery 17 and inductance coil 18, the repeater coilprimary 5 is connected through the condensers 19,

19 whose function is to prevent the passage of direct current through the winding 5.. Artificial lines 20, 20, which may be of a well-known construction, are provided, said artificial l stantially the same impedance as the telephone line over the range of telephonic frequencies. Said artificial lines are provided in order that inductive effects from the output side of one repeater 11, impressed through the'coil 5, shall not create any difference of potential between the conductors 8' and 9. This condition is necessary in order that the output side of one repeater shall notimpress disturbances on the input side of the other repeater, and thus cause sustained interaction or singing between the repeaters 11, 11. The function of' the filters 1*, 1 than those.

necessary for the telephonic transmiss on of intelligible speech from being transmitted from the telephone line to ines having subis to prevent currents other frequency wave-filter 1 may be omitted from the circuit when conditions are such as not to require the protection of the repeater from low frequency disturbances.

It is well known that high frequenc induction or inductive disturbances mi itate seriously against the satisfactory operation of. telephone repeaters, particularly of the vacuum tube type, such as are shown in Figs. 10 and 11. It is also well known that low frequency disturbances, such as those due to superposed or composited telegraphic impulses are equally objectionable. My invention prevents either high frequency or low frequency disturbances from affecting the repeater by inserting wave-filters between the telephone lines and the repeaters, as shown, for example, in Figs. 10 and 11. In this particular case, said wave-filters are designed to transmit all frequencies lying within the limiting frequencies,-say between 200 and 2200 cycles per second, necessar for intelligible, telephonic transmission 0 speech, while extinguishing currents of all frequencies lying above 2200 and below 200 cycles per second.

A further advantage attending the employment of the wave-filter with the repeater circuits lies in the fact that the balancing artificial line need simulate the impedance characteristics of the telephone lines only over the limited range of frequencies necessary for intelligible telephonic transmission of speech, which permits of a more simple, efficient and economical artificial line.

I claim:

1. The combination with cuit and a repeater therefor, of a wave filter inserted in circuit between said signaling circuit and said repeater for transmitting, with tenuation, betweensaid signaling circuit and repeater, sinusoidal currents of all frequencies between an upper pre-assigned limiting frequency and a lower pre-assigned limiting frequency of a predetermined range of fre-- quencies, while attenuating and approximately extinguishing currents of neighboring frequencies lying outside of said range.

'2. The combination with a telephone line and a repeater therefor, of a wave filter inserted in circuit between said line and said repeater for transmitting, negligible attenuation, between said line. and repeater, sinusoidal currents of allfrequenciesbetween the upper and lowerl lim'its of the frequencies necessary for the telephonic transmission of intelligiblespeech, while attenuating and approximately extinguishing currents of neigh outside of said limits.

3. The combination with a transmission line, of an artificial line, a repeater, and a a signaling cir--' with practically boring frequencies lying wave-filter adapted to transmit with negligible attenuation a definite range of frequencies inserted in circuit between said line and said repeater for'prescribing the range of frequencies to be transmitted by said repeater, substantially as described.

4. The combination with a transmission line, of a repeater normally capable of transmitting currents of, all frequencies, a wave:- filter' for limiting to a definite range frequencies amplified by said repeater, and an artificialline simulating the impedance characteristics of said transmission line only over said limited range of frequencies, substantially as described.

5. The combination with a telephone line, of a vacuum tube repeater, a wave-filter for limiting the range of frequencies transmitted by said repeater, and an artificial line simulating the impedance characteristics of said telephone line only over said limited range of frequencies, substantially as described.

6, The combination with a telephone line and a telephone repeater therefor, of an electric wave-filter inserted in circuit between said line and the input side of said repeater, said filter consisting of a connecting line having lumped inpedance in series with said connecting line and lumped impedance in shunt across said connecting line, said impedances having precomputed values dependent upon the upper limiting frequency and the lower limiting frequency of a range of frequencies necessary for telephonic transmission of intelligible speech, the values of said series and shunt impedances being so proportioned that said connecting line transmits with practically negligible attenuation, from the telephone line to the repeater, sinusoidal currents of all frequencies within said range of frequencies, while attenuating and approximately extinguishing. currents of neighboring frequencies lying outside. of said range.

7. The combination with a telephone line and a vacuum tube repeater cooperating therewith, of an electric wave-filter inserted in circuit between said line and the input side of said repeater, said filter consisting of a connecting line composed of a plurality of sections, each section including a capacity element and an inductance element, one of said elements of each section being in series with said connecting line and the other in shunt across said connecting line, said capacity and inductance elements having precomputed values dependent upon the upper limiting frequency and the lower limiting frequency of a range of frequenci-s necessary for telephonic transmission of intelligible speech, the-values of said capacit and inductance elements being so proportioned that said connecting line transmits with practlcally negligible attenuation, from the telephone line to said vacuum repeater, sinuand approximately extinguishing currents of neighboring frequencies lying outside of said range.

8. The combination with a signaling circuit and a translating device'therefor, of a wave filter inserted in circuit between said signaling circuit and said translating device, said filter including impedances having Values depending uponthe upper limiting frequency and the lower limiting frequency of, a. prescribed range ,of frequencies, the valuesof said impedances being so proportioned that said filter transmits with practically uniformly negligible attenuation, between said signaling circuit and translating device, sinusoidal currents of all frequencies within'said range of frequencies; while attenuating and approximately extinguishing currents of neighboring frequencies lying outside'of said range.

9. In combination with a telephone. line, a repeater normally capable of-transmitting all frequencies with equal efliciency, a wave filtering apparatus to limit the range of frequenciesato be transmitted from the line to the repeater, and a. balancing network capable of balancing the telephone line for frequencies within the range so limited but incapable of balancing the line for frequencies outside such limitation but within the normally effective range of the amplifier.

10. The combination with a transmission line and a. repeater therefor, of a wave filter inserted in circuit between said line and said repeater, said filter consisting of a connecting line having lumped impedances in series with said connecting line and lumped impedance in shunt across said connecting line, said impedances having values dependent upon the upper limiting frequency and the lower limiting frequency of a prescribed range of frequencies, the values of said series and shunt impedances-being so proportioned that said connecting line transmits with practically negligible attenuation, between said line and repeater,sinusoidal currents of all frequencies within said range of frequencies, while attenuating and approximately extinguishing currents of neighboring frequencies lying outside of said range.

In testimony whereof, I have signed my name to this specification in the presence of two subscribing witnesses, this 25th day of May-1916.

GEORGE, A. CAMPBELL. Witnesses:

R. S. SUTLIFFE, RALPH W. WOLF. 

